KR20090038309A - Electrode for secondary battery, manufacturing method thereof, and secondary battery employing the same - Google Patents

Abstract

An electrode for a secondary battery is provided to improve the capacity of electrode and cycle of a battery by improving the uniformity of an active material layer through the printing of low point ink. An electrode for a secondary battery comprises a current collector(10) and an active material layer formed by printing and drying ink(11) having the viscosity of 500 mPa . s on the current collector. The surface roughness Ra the current collector is 0.025-1.0 micron. The thickness the active material layer is 0.1-10 micron. The current collector is surface-treated with UV or the plasma.

Description

Electrode for secondary battery, method for manufacturing same and secondary battery employing the same {Electrode for secondary battery, manufacturing method, and secondary battery employing the same}

The present invention relates to a secondary battery electrode, a manufacturing method thereof and a secondary battery employing the same.

As a battery that is used as a power source for mobile devices or for power storage, various forms are used depending on the intended use and environment. Primary batteries such as zinc manganese batteries have to be used and discarded once, while secondary batteries such as lead storage batteries, nickel metal hydride batteries, nickel cadmium batteries, and lithium ion batteries can be used repeatedly while charging and discharging.

Recently, with the continuous development of electronic technology, the demands of consumers of electronic devices are diversified, and various demands on batteries are increasing. In particular, with the emergence of electronic devices that can bend or bend, it is necessary to develop technologies that can increase not only battery performance but also battery thickness and flexibility. In addition, to cope with various device designs, a process technology that can easily change a battery design is required.

The electrode active material layer of a lithium ion battery is mainly formed by the slurry coating method. However, when the slurry coating method is used, a thick active material layer having a thickness of several tens of μm is formed, so that the electrode lacks durability against bending and bending, and it is difficult to change the shape of the electrode, and thus it is difficult to cope with various designs.

On the other hand, the thin film battery can be manufactured by a thin film manufacturing process such as sputtering, it is troublesome to manufacture and high production cost, there is a problem that the process time is long and heat treatment process is required. In order to solve this problem, a method of forming an electrode using ink for inkjet printing has been proposed (CN 1215585C).

By the way, when the electrode active material layer is formed according to the above method, the thickness of the active material layer is different, the overall non-uniform active material layer is formed, there is much room for improvement.

The present invention is to provide a secondary battery electrode employing an active material layer in which the uniformity of the active material layer is improved by printing a low-viscosity ink, a manufacturing method thereof and a secondary battery having improved electrode capacity by employing the same.

According to an embodiment of the present invention, a current collector and an active material layer formed by printing and drying an ink having a viscosity of 500 mPa · s or less on the current collector,

The current collector is provided with a secondary battery electrode, characterized in that the surface roughness Ra is 0.025 to 1.0 ㎛.

The active material layer has a thickness of 0.1 to 10 μm. And the current collector may be UV or plasma surface treatment.

In the present invention, the active material layer may include an active material, a conductive agent, and a binder, and may include a dispersant.

According to another embodiment of the present invention, the method comprising: preparing an ink having a viscosity of 500 mPa · s or less including an active material, a conductive agent, a binder, and a solvent; And

Provided is a method of manufacturing an electrode for secondary batteries, including forming an active material layer by printing and drying the ink on a current collector having a surface roughness Ra of 0.025 to 1.0 μm.

The printing is carried out according to the inkjet printing, gravure printing, flexography printing, offset printing, screen printing or doctor blade printing.

The current collector having the surface roughness Ra of 0.025 to 1.0 µm can be obtained by polishing, rolling, etching, laser processing or sand blasting or by electroless plating, electrolytic plating or printing. You can get it.

According to another embodiment of the present invention, a secondary battery having the above-described electrode is provided.

Hereinafter, the present invention will be described in more detail.

 When the ink having low viscosity is printed on the current collector when the electrode active material layer is formed, ink droplets printed on the current collector are easily moved due to the low viscosity of the ink, and the ink droplets have surface energy of the current collector surface and surface tension of the ink. The behavior depends on the form. If the surface energy of the current collector is not large enough and the surface tension of the ink is not sufficiently low, the ink droplets on the current collector will aggregate in a narrower area as the contact angle becomes larger. When drying in this state to form the active material layer, the thickness of the formed active material layer varies depending on the position, thereby forming an overall non-uniform active material layer.

When the current collector surface energy is low and the surface tension of the ink is large, the ink tends to agglomerate in the form of round droplets, and the ink droplets are separated from each other to form a large contact angle on the surface. On the contrary, when the surface energy of the current collector is large and the surface tension of the ink is small, the ink tends to increase the contact area with the surface of the current collector so that ink droplets spread and maintain a smaller contact angle with the surface. At this time, when the ink droplets are sufficiently large, a film of ink is formed over the entire area where the ink is printed while the adjacent ink droplets are connected to each other, and uniformly drying the ink droplets can obtain an active material layer having improved uniformity.

In order to increase the uniformity when printing the low viscosity ink to form the active material layer of the electrode, it is effective to increase the surface energy of the current collector or lower the surface tension of the ink.

However, there are limitations in the properties of the materials that can be used to combine the inks, and in order to meet the various properties of the inks such as the viscosity, dispersibility, and drying properties required for printing, there are many ways to precisely control the properties of the surface tension. Difficulties follow In addition, in the case of inkjet printing, in order to prevent contamination of the outside of the inkjet nozzle and to increase the uniformity when discharging the ink, it is rather disadvantageous that the ink has a low surface tension. There are several restrictions.

Accordingly, according to the present disclosure, the surface roughness of the current collector is increased by controlling the surface roughness of the current collector, and the low-viscosity ink is printed on the current collector having such a high surface energy to improve the uniformity of the active material layer. In this case, the process of forming an active material layer becomes simple.

According to the disclosure of the present invention, the viscosity of the low viscosity ink for forming the electrode active material layer is 500 mPa · s or less, preferably 2 to 300 mPa · s, and more preferably 5-100 mPa · s. If the viscosity of the ink exceeds 500 mPa · s, it becomes difficult to spread the ink droplets on the current collector, making it very difficult to form an active material layer having a uniform composition.

1A to 1C are diagrams for describing a principle in which an active material layer is uniformly formed on a current collector having high surface energy according to an embodiment of the present invention.

Referring to FIG. 1A, when the ink droplets 11 are transferred onto the current collector 10 through a printing process, the low-viscosity ink 11 may be agglomerated with each other on the current collector 10.

Referring to FIG. 1B, when the surface energy of the current collector 10 is high, the contact angle of the droplets of the ink 11 becomes small, which causes the ink 11 to spread on the current collector.

As can be seen from FIG. 1C, as the droplets of spread ink 11 are connected to each other, a uniform film is formed on the current collector 10, thereby obtaining an active material layer having improved uniformity.

Uniformity of the active material layer in the electrode is very important in battery characteristics. If the active material layer of the electrode is not uniform, the thickness of the active material layer varies depending on the position on the electrode. In this case, even when a uniform pressure is applied to a predetermined area of the electrode from the outside, the active material layer receives different pressure depending on the position. That is, greater pressure is applied to the thicker active material layer, and smaller pressure is applied to the thinner active material layer. In other words, since the pressure is concentrated in a thick position of the active material layer and is subjected to a greater pressure, the substrate, the current collector, the active material layer, the separator, and the like, which are located at this position, are all subjected to concentrated pressure, thereby risking physical damage to the battery. Will grow. Uniformity of the electrode active material layer is also important in terms of durability against bending. When the electrode is bent or bent, the thicker portion of the active material layer is subjected to relatively greater stress as compared to the thinner portion. Therefore, the thicker active material layer is more easily peeled off may degrade the performance of the electrode.

In addition, when the thickness and composition of the active material layer of the electrode is not uniform, there is a problem that the battery performs its function as a battery through an intrinsic electrochemical reaction. In addition, a thicker region and a thinner region of the active material layer coexist. In this case, a larger amount of the active material is present in the thicker region, and because the thickness of the active material layer is thicker, some active materials in this region are more active than other active materials. The distance from the current collector is farther away. Therefore, a relatively large amount of active material flows in a region in which the active material layer is thick, so that more current flows, and some active materials in this region have a larger electrical resistance from the current collector to the active material. That is, if the uniformity of the active material layer is poor, more reaction occurs in some regions when the electrochemical reaction occurs, and more heat is generated due to more load due to the greater electrical resistance. As a result, the active material of some regions may cause an irreversible reaction faster than the active materials of other regions, resulting in poor cycle characteristics of the battery.

According to the disclosure of the present invention, the uniformity of the electrode active material layer is improved as described above, thereby improving the capacity of the electrode, the cycle characteristics of the battery, and the like.

According to one embodiment of the present invention, the total thickness of the electrode active material layer is 0.1 to 10 μm, which is very thin compared to the thickness of the active material layer obtained by the conventional slurry method, and there is almost no thickness variation of the active material layer. As such, since the thickness is small and the variation is small, it is possible to construct a thin battery as compared with the conventional case, and there is an advantage in that durability against bending is excellent.

Hereinafter, a method of manufacturing a secondary battery electrode according to an embodiment of the present invention will be described.

First, an active material, a conductive agent, a binder, a dispersant, and a solvent are mixed to prepare an ink which is a composition for forming an active material layer. And the viscosity of the ink is preferred that the viscosity is not more than 500mPa · s, and particularly preferably 5 to 100mPa · s.

The active material may be any of conventional oxide particles used as an electrode active material of a secondary battery.

Specific examples of the active material include Li-Co-based composite oxides such as LiCoO ₂ , Li-Ni-based composite oxides such as LiNiO ₂ , Li-Mn-based composite oxides such as LiMn ₂ O ₄ , LiMnO ₂ , and Li ₂ Cr ₂ O ₇ , Li-Cr complex oxides such as Li ₂ CrO ₄ , Li-Fe complex oxides such as LiFeO ₂ , LiFePO ₄ , Li-V complex oxides, Li-Ti complex oxides such as Li ₄ Ti ₅ O ₁₂ Transition metal oxides such as, SnO ₂ , In ₂ O ₃ , Sb ₂ O _3, and carbon-based materials such as graphite, hard carbon, acetylene black, and carbon black.

The conductive agent may be acetylene black, carbon black, graphite, carbon fiber, carbon nanotube, or the like as a material for improving conductivity of the active material. And the content of the conductive agent is preferably 1 to 15 parts by weight based on 100 parts by weight of the active material.

As the solvent, deionized water is used as a main component, and alcohols such as ethanol, methanol, butanol, propanol, isopropyl alcohol, isobutyl alcohol, and N-methyl-2-pyrrolidone are mixed to control the drying rate. Solvent is used. And the content of the solvent is preferably 100 to 20000 parts by weight based on 100 parts by weight of the active material.

The dispersant used in the present invention serves to uniformly disperse the active material and the conductive agent. Specific examples of the dispersant include fatty acid salts, alkyl dicarboxylates, alkyl sulfate ester salts, polyhydric acid ester alcohol salts, alkyl naphthalene sulfate salts, alkylbenzene sulfate salts, alkyl naphthalene sulfate salts, alkyl sulfon succinate salts, naphthenate salts and alkyl ethers. Carboxylate, Acylate Peptide, Alpha Olefin Sulfate, N-Acyl Methyl Taurine Salt, Alkyl Ether Sulfate, Secondary Polyalcohol Ethoxy Sulfate, Polyoxyethylene Alkyl Peryl Ether Sulfate, Monoglysulfate, Alkyl Ether Phosphate Ester Salt, Alkyl Phosphoric acid ester salt, alkylamine salt, alkylpyridium salt, alkylimidazolium salt, fluorine- or silicone-acrylic acid polymer, polyoxyethylene alkyl ether, polyoxyethylene sterol ether, lanolin derivative of polyoxyethylene, polyoxyethylene / Polyoxypropylene copolymer, polyoxyethylene sorbitan fatty acid ester, monoglyceride fatty acid Sterrose, sucrose fatty acid ester, alkanolamide fatty acid, polyoxyethylene fatty acid amide, polyoxyethylene alkylamine, polyvinyl alcohol, polyvinylpyridone, polyacrylamide, carboxyl group-containing water-soluble polyester, hydroxyl group-containing cellulose type Resin, acrylic resin, butadiene resin, acrylic acid type, styrene acryl type, polyester type, polyamide type, polyurethane type, alkyl betamine, alkylamine oxide, phosphatidylcholine, or mixtures thereof. Herein, the content of the dispersant is preferably 0.1 to 50 parts by weight based on 100 parts by weight of the active material. If the content of the dispersant is out of the above range, it is not preferable because the dispersing effect of the active material and the conductive agent is lowered or the relative content of the active material or the conductive agent is reduced and the electrode performance is lowered.

The binder serves to impart a binding force between the ink and the current collector after printing. Examples of such binders include polyvinyl alcohol, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene air And at least one selected from coalescing and carboxymethyl cellulose (CMC). And the content of the binder is preferably 1 to 10 parts by weight based on 100 parts by weight of the active material. If the content of the binder exceeds the above range, the relative content of the active material is reduced to decrease the capacity of the electrode. If the content of the binder is less than the above range, the binding force between the active material layer and the current collector is reduced, which is not preferable.

The ink may be further added a buffer for maintaining the stability of the ink and adjusting the appropriate pH. As the buffer, one or more amine compounds selected from trimethylamine, triethanolamine, diethanolamine, ethanolamine or sodium hydroxide and ammonium hydroxide can be used. The content of the buffer is preferably 0.1 to 50 parts by weight based on 100 parts by weight of the active material.

When preparing the ink, a suitable amount of the active material, the conductive agent, the solvent, the dispersant, and the binder described above are mixed, and the ball mill or the bead mill is sequentially performed, and then filtered using a filter. At this time, the filter is used to remove impurities using, for example, a membrane syringe filter having a pore diameter of 0.45 to 5 mu m.

Subsequently, printing was performed on ink collectors, gravure printing, flexography printing, offset printing, screen printing or doctor blade printing using the ink obtained according to the above process on the current collector on the surface roughness Ra of 0.025 to 1.0 μm. After the drying process, it is dried to form an active material layer. The drying is carried out here at a temperature of 40 to 300 ° C.

According to an embodiment of the present invention, the current collector may print and dry ink on the current collector in a state of being attached to a separate support. In this case, a polyethylene terephthalate film, a mylar film, or the like is used as the support. After the completion of the printing process, the support is separated.

The total thickness of the active material layer thus formed is 0.1 to 10 탆, which is very thin.

 The current collector having a surface roughness Ra of 0.025 to 1.0 µm used in the present invention can be obtained according to various methods. For example, it can manufacture by forming an unevenness | corrugation etc. in the surface by a grinding | polishing process, the method of using a rolling roll, an etching process, a laser process, or a sand blast process. In addition, the current collector may be manufactured by using electroless plating, electrolytic plating, or printing in the production of the current collector. This method is a method commonly used in manufacturing a current collector.

The polishing refers to a process of forming irregularities on the surface of the current collector using abrasive paper. In addition, a method of using a rolling roll is a process of forming irregularities in the current collector by using the unevenness of the surface form present in the rolling roll, and the etching treatment is to control the roughness of the current collector surface by using an acid solution or the like which is an etching solution. The laser treatment is to irradiate a laser on the surface of the current collector to form irregularities on the surface of the current collector. Sandblasting is to spray sand on the current collector surface using compressed air to form irregularities on the current collector surface.

The shape, size, etc. of the unevenness formed on the current collector to control the surface roughness of the current collector are not particularly limited. Although the shape of the convex part of the unevenness | corrugation of the surface of an electrical power collector is not specifically limited, For example, it is preferable that it is an awl shape.

The current collector according to the present invention has a surface roughness Ra of 0.025 to 1.0 mu m as described above, preferably 0.03 to 0.5 mu m, more preferably 0.04 to 0.3 mu m.

In addition, the current collector having the above-described surface roughness may be further subjected to UV or plasma surface treatment. Through such a surface treatment, when the surface energy of the current collector is increased to form an active material layer with a low viscosity ink, the uniformity of the active material layer becomes higher.

The current collector used in the present invention can be used as long as it can form the active material layer on the upper portion of the good adhesion, as a specific example, at least one selected from copper, aluminum, stainless, molybdenum, tungsten, tantalum is used. .

It is preferable that a collector is thin, and it is preferable that it is metal foil, and it is preferable that the thickness is 1 nm-30 micrometers.

According to one embodiment of the present invention, the finally obtained active material layer includes an active material, a conductive agent and a binder. In the case of adding a dispersant in ink production, the dispersant may be contained in the finally obtained active material layer.

By using the electrode obtained according to the present invention, the uniformity of the active material layer is improved, and when it is adopted, a secondary battery having improved electrode capacity can be manufactured.

The secondary battery may be a power source for portable portable devices such as mobile phones, PDAs, and PMPs, a power source for driving motors such as high-power hybrid vehicles, and electric vehicles, power sources for flexible display devices such as e-inks, electronic papers, and E-pads; In the future, there is a high possibility of application as a micro battery for powering an integrated circuit device on a printed circuit board (PCB).

Specific examples of the secondary battery according to the present invention include a lithium secondary battery.

In the lithium secondary battery, the cathode uses a lithium composite oxide containing lithium in the active material mentioned in the description of the method for manufacturing the electrode described above as the active material. The anode uses a carbon-based material such as graphite, hard carbon, acetylene black, carbon black, lithium composite oxide or lithium metal thin film itself.

As the electrolyte membrane, any one commonly used in a lithium secondary battery such as a vinylidene fluoride-hexafluoride copolymer electrolyte membrane, a polyethylene membrane, a polypropylene membrane, or the like can be used.

The lithium secondary battery may be fabricated by interposing an electrolyte membrane between the cathode and the anode, and assembling according to a method commonly used in a lithium secondary battery.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the present invention is not meant to be limited only to the following examples.

Example 1

Whole  Ready

An aluminum foil having a thickness of 15 μm was prepared as a current collector, and abrasive paper having powder abrasive grain # 800 was used to control the surface roughness. In polishing, the aluminum foil was placed on a flat glass plate and polished with abrasive paper for 1 minute each. The polished current collector was cut into a size of 10 cm in width and 8 cm in length, and then attached to a 100 µm polyethylene terephthalate (PET) film having a thickness of A4 paper. The ready-to-print collector surface was cleaned with a wiper moistened with ethanol.

Surface roughness  Measure

The unpolished aluminum foil or the polished aluminum foil was adhered to a glass substrate having a surface roughness Ra of 0.5 nm, and then surface roughness was measured. Measured using KLA-Tencor surface profiler P-16, X scan size is 500um, scan rate is 20um / s, sampling rate is 100Hz, applied force is 1.0 It was measured by setting the mg, and the average value was taken five times.

Manufacture of ink

Water 58.3 g, ethanol 5.7 g, ethylene glycol 30.9 g, diethylene glycol 1.9 g, triethanolamine 0.38 g, LiFePO ₄ 1.52 g, dispersant EFKA4580 (Shiba Shiva) 0.42 g, acetylene black 0.19 g, methyl cellulose (CMC) 0.05 An ink having a composition of g was prepared and filtered by a membrane syringe filter having a pore diameter of 5 mu m to prepare an ink. At this time, the viscosity of the ink was about 20 mPa · s.

Filling of ink

After removing the cover adhered to the top of the ink cartridge, all the ink filled therein was removed and washed. The sponge inside was also thoroughly cleaned, dried and placed back into the cartridge. The ink prepared in the above procedure was filled into a syringe, and injected into the cartridge through a syringe needle.

After the injection was completed, the cartridge cover was closed, and the air pressure outside the nozzle was lowered to allow the ink inside the cartridge to flow out through the nozzle to remove air from the cartridge, and then wipe the ink on the bottom of the nozzle. The cartridge thus completed was attached to the hp deskjet 5550 printer.

print

A black pattern of 8 cm in width and 6 cm in length was designed, and the active material ink was printed on the current collector by supplying a PET film with aluminum foil as a current collector.

Immediately after printing, the resultant was dried for 10 minutes at 80 ° C., and again printed and dried in the same manner for 15 times to complete the electrode. The finished electrode was dried in a vacuum oven at 120 ℃ for 2 hours and then rolled using a rolling roll.

Electrode evaluation

The completed electrode was subjected to initial capacity evaluation through coin cell production and charge / discharge tests, which are methods used to evaluate ordinary secondary battery electrodes.

Example 2

In the polishing process of the current collector, a secondary battery electrode was prepared in the same manner as in Example 1 except that the abrasive paper having powder abrasive grain # 120 was used instead of the abrasive grain having powder abrasive grain # 800.

Comparative Example 1

A fuel cell electrode was produced in the same manner as in Example 1 except that the current collector was not polished.

Comparative Example 2

In the polishing treatment of the current collector, the same procedure as in Example 1 was carried out except that the abrasive paper having powder abrasive grain # 60 was used instead of the abrasive grain having powder abrasive grain # 800.

2 and 3 are photographs showing the surface state of the active material layer of the electrode in the electrode prepared according to Example 1 and Comparative Example 1, respectively.

 Referring to FIG. 2, in Example 1, the active material layer was confirmed to be uniformly formed. In Comparative Example 1, as shown in FIG. The active material layer was unevenly applied so that the silver aluminum bottom was revealed.

In the electrodes according to Examples 1-2 and Comparative Examples 1-2, the surface roughness of the current collector and the capacity per gram of the electrode were investigated and shown in Table 1 below.

TABLE 1

division Surface roughness adjustment method Surface Roughness Ra (㎛ ) of Current Collector Capacity per gram of electrode (mAh / g) Remarks Example 1 # 800 abrasive paper used 0.22 130.1 Example 2 # 120 used abrasive paper 0.82 122.1 Comparative Example 1 No polishing treatment 0.02 121.4 Comparative Example 2 # 60 using abrasive paper 1.2 - Current collector damage during polishing

As can be seen from Table 1, the electrodes of Examples 1 and 2 had an increase in electrode capacity per area compared with that of Comparative Example 1. On the other hand, in Comparative Example 2, a normal electrode could not be manufactured because the current collector was damaged by applying excessive physical stress to the current collector to obtain a current collector having a high surface roughness value.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary and will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible.

1A to 1C are diagrams for explaining a principle in which an active material layer is uniformly formed on a current collector having high surface energy according to one embodiment of the present invention;

2 is a photograph showing the surface state of the active material layer of the electrode in the electrode manufactured according to Example 1 of the present invention,

3 is a photograph showing a surface state of an active material layer of an electrode in an electrode manufactured according to Comparative Example 1. FIG.

Claims (9)

A current collector and an active material layer formed by printing and drying an ink having a viscosity of 500 mPa · s or less on the current collector, The current collector has a surface roughness Ra of 0.025 to 1.0 μm, the electrode for secondary batteries. The method of claim 1, wherein the active material layer is a secondary battery electrode, characterized in that the thickness of 0.1 to 10㎛. The electrode of claim 1, wherein the current collector is surface treated with UV or plasma. Preparing an ink having a viscosity of 500 mPa · s or less including an active material, a conductive agent, a binder, and a solvent; And A method of manufacturing an electrode for secondary batteries, the method comprising forming an active material layer by printing and drying the ink on a current collector having a surface roughness of Ra of 0.025 to 1.0 μm. The method of claim 4, wherein the current collector is surface-treated using UV or plasma. The method of claim 4, wherein the printing is performed by inkjet printing, gravure printing, flexography printing, offset printing, screen printing, or doctor blade printing. The collector of claim 4, wherein the current collector having a surface roughness of Ra of 0.025 to 1.0 µm is obtained by a polishing process, a method using a rolling roll, an etching process, a laser treatment, or a sand blasting process. Manufacturing method. The current collector of claim 4, wherein the surface roughness of Ra is 0.025 to 1.0 μm, A method for producing an electrode for secondary batteries, characterized in that it is obtained by electroless plating, electroplating or printing. A secondary battery comprising the electrode according to any one of claims 1 to 3.

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